roasted barley in AG

How much more 'bitter' would a beer be by upping the roasted barley amount in a stout from 2% to 6%? Sorry for the short question, typing on my Blackberry in a plane right now

A little roasted barley goes a long way in any beer. The bitter raosted flavor comes through with even small amounts. If you triple the amount of roasted barley it may still turn out to be a good beer, but chances are that the bitterness of the roasted barley would completely dominate the taste profile. Usually you would want to keep the roasted barley precentage at 5% or less, so 6% would not be too crazy, but is more than enough to completely change the taste of the original recipe.

Ed